Technical Field
The present application generally relates to measurement of the flux, current, or charge of a beam, and more particularly, to measurement of flux, current, or integrated charge of beam having low energy particles or ions.
Description of the Related Art
Beams of charged particles have many technological utilities. These beams have various attributes. One such attribute is the flux. The flux expresses the number of particles in the beam per unit area per unit time. The flux may be expressed in units of particles per square-centimeter-second (particles/cm2-sec). Another attribute is the beam current. The beam current expresses the flow of electrical charge and may be expressed in amperes (A), where 1 A is equivalent to 1 coulomb per second (C/sec). One coulomb (C) is equivalent to the charge of approximately 6.242×1018 electrons. Beam charge is yet another attribute and expresses the current multiplied by time. The energy associated with moving an ion with a single unit of electrical charge, for example one electron, across a potential of 1 volt (V) is defined as one electron volt (eV). The energy associated with moving one coulomb of charge across a potential of 1 V is defined as one joule (J).
A charged particle may be an elementary particle (e.g., a proton), any type of ion (e.g., He−), or a combination of particles, which bear an electrical charge such that they can be deflected using an electrical or magnetic field. The term ion, as used herein, collectively refers to any type of particle with an electrical charge.
Flux, beam current, or integrated charge measurement finds applications in many areas, including medicine, semiconductor technology, radiations technology, and other fields. Some non-limiting examples include cancer therapy, ion implantation, parity bit setting, soft error rate detection, Rutherford Backscatter Spectroscopy (RBS), etc.
Flux may be measured with various detectors. Specifically, flux may be calculated from an ion count which can be measured by surface barrier detectors. Such detection is possible when the beam energy is of the order of 1 MeV or larger.
Faraday cups may also be used to measure ion count. Faraday cups are susceptible to errors from noise, from leakage currents, and from lack of electron suppression, among other things. Theoretically, some of these errors can be overcome by making the depth of the Faraday cup infinitely deep or reducing the electrical noise.